Current contra angle handpieces are designed either to only rotate the file or to move the file up and down without rotating it. Each motion has its own separate advantages. By rotating the file, due to the file fluting, this allows the file to engage with the root canal and clean and shape more efficiently. The disadvantage to pure rotation movement is the susceptibility to over torque the file while performing a root canal procedure. If the file begins to bind in the canal, it can increase the potential for the file to either unwind or separate. Also, by having pure rotation, if the file is going around a curve and is held at that curve too long, cyclical fatigue can cause the file to separate. By having only an up and down motion without any rotation of the file, it prevents the file from over torque. It also prevents the file from experiencing cyclical fatigue failure due to extensive rotational motion while going around a curve. The disadvantage of just up and down motion is that the cutting efficiency is significantly reduced due to the design of the file and its fluting.
There are many commercially available contra angle handpieces that have the capability of rotating the file clockwise, counterclockwise, or in reciprocation motions when connected to an endodontic motor (Aseptico, ATR, Sirona). These contra angle handpieces are available in many different gear ratios based upon the desired RPM capabilities of the clinician. Also, there are commercially available contra angle handpieces that have the capability of vertically oscillating the file in an up and down motion without rotation (EndoPulse, ReDent). U.S. Pat. No. 8,172,572 discusses a handpiece design that has a reciprocating motion parallel to the tool axis at a first frequency of oscillations per minute and rotates about the tool axis at a frequency at a second frequency of rotations per minute, wherein said first frequency is at least one order of magnitude greater than said second frequency. It goes on to state that the tool holder rotates through a rotational step of no more than a fortieth of a revolution about said tool axis. It also states that the first frequency (motion parallel to the tool axis) is at least two orders of magnitude greater than said second frequency (rotation about the tool axis). This type of design is primarily intended to vertically oscillate at a much greater magnitude than it rotates. By having this type of motion, most conventional rotary files would not be able to be used with this type of contra angle design because the rotation is not balanced with the vertical oscillation. Most conventional file designs would prefer no more than a ratio of 8 to 1 where there are 8 vertical oscillations for every rotation of the file. U.S. Pat. Nos. 4,175,324; 5,169,312; 5,454,718; and 5,453,008 discuss using an eccentric shaft or pin, which is driven by the motor to cause the file in the contra angle to move up and down. This is perfectly fine for a concept where the file is only moving in a vertical motion and not rotationally. The problem comes when the desire is for the file to rotate as well. Therefore, a separate component would have to be added to have the file rotate while driven by the motor. U.S. Pat. No. 5,145,369 discusses a cam mechanism where FIG. 60 is rotating along the top of the contra angle and a restoring spring is used to apply constant pressure to the cam mechanism thus allowing it to rotating while moving up and down. The key in this design is that the cam mechanism will generate friction if not lubricated well and may cause the cam mechanism to wear down over time depending on the spring constant of the restoring spring. U.S. Pat. Nos. 6,106,290 and 4,289,849 discusses a hand piece with groove portions or a L-shaped link arm which allows the file to reciprocate both vertically and in rotation. The problem with this design is that the file is never allowed to fully rotate 360° which will limit the cutting efficiency of the file as it progresses within the root canal.
Most current contra angle handpieces are designed either to only rotate the file or to oscillate the file up and down without rotating it. Each motion has its own separate advantages. By rotating the file, due to the file fluting, this allows the file to engage with the root canal and clean and shape more efficiently. The disadvantage to pure rotation movement is the susceptibility to over torque the file while performing a root canal procedure. If the file begins to bind in the canal, it can increase the potential for the file to either unwind or separate. Also with pure rotation, some file designs allow the file to screw into the canal thus causing the clinician to lose control of the progression of the file. This can lead to transportation or apical zipping of the canal. Also, by having pure rotation, if the file is going around a curve and is held at the curve too long, cyclical fatigue can cause the file to separate. By having only an up and down vertical motion without any rotation of the file, it prevents the file from over torque. It also prevents the file from experiencing cyclical fatigue failure due to extensive rotational motion while going around a curve. The disadvantage of just up and down motion is that the cutting efficiency is significantly reduced due to the design of the file and its fluting. By having a motion of the file that is both in rotation as well as axial movement up and down, it allows the file to clean and shape efficiently while reducing the torque and cyclical fatigue exposure on the file.
As such, the present invention attempts to overcome these problems by providing a handpiece configured to achieve a motion (e.g., a motion of a file) having both rotation (e.g., clockwise, counterclockwise, or a combination of both movement about the file axis) as well as oscillation (e.g., axial movement up and down) dual motion. This dual functionality allows the file to clean and shape efficiently while reducing the torque created on the file and cyclical fatigue exposure.